1. Field of the Invention
The invention refers to a roof hook for transferring the high loads associated with solar power systems into the substructure of roofs. Solar power systems can be based on photovoltaic modules or on solar collectors which are either mounted on support frames connected to the roof hook or are connected directly to the roof hook.
2. Description of the Related Art
The roof hook is passed through the roof covering and connected to the substructure of the roof, normally by means of holding screws or a form-fit connection (DE 20 2007 011 314 U1). The material used is bent flat steel sections which are usually made of stainless steel. A roof hook made of cast aluminium is known from EP 1 764 454 A2. An aluminium roof hook, without further specification as to the type of aluminium, is also disclosed in DE 20 2005 004 348 U1.
Furthermore, two-part roof hooks are known in the state of the art. They consist of a base part, which is connected to the roof substructure, and the hook part as such, which is passed through the roof covering and connected to the base part on the one hand and to the support frame for the solar modules on the other.
The base part and the hook part can be connected to each other rigidly, e.g. by welding, or releasably, e.g. by means of a bolt-nut connection. The term “two-part” as used in the present invention means a releasable connection.
The hook part can also be made in two parts to allow for additional height adjustment during mounting.
The general adjustment options are described in DE 20 2005 009 U1.
According to DE 201 19 478 U1, the releasable connection between the base part and the hook part is achieved by means of a screwed connection, which can include a height adjustment option according to DE 20 2005 019 897 U1.
As an alternative, form-fit connections between the base part and the hook part have been described, mainly with a view to lateral adjustment, i.e. displacement parallel to the mounting plane of the base part (DE 102 13 902 A1, DE 10 2005 058 065 A1, DE 20 2005 004 348 U1).
The above structures of two-part roof hooks essentially have in common that the base part comprises a portion which is perpendicular to the mounting plane on the roof substructure and to which the hook as such is flange-connected. Due to the lever arm of the hook part, this angle is subjected to high loads, which has led manufacturers to fall back on a well known principle, namely to arrange strengthening ribs or strengthening webs between the portion of the base part which is located in the mounting plane and the portion which is perpendicular thereto (DE 20 2006 009 674, EP 1 764 454 A2).
This measure to improve the load-bearing capacity entails higher production costs during the manufacture of roof hooks as a casting process has to be employed or additional shaping steps for integrally forming the webs are required.
The object of the invention is to propose a two-part roof hook, the base part of which has a high load-bearing capacity without requiring single strengthening webs or ribs and can be made of aluminium or an aluminium alloy.